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The Burning Sunscreen Question: Which SPF Is Best?

You’ve seen the vast array of sunscreens lining the shelves in stores. From SPFs that dip as low as 2 to packages with numbers as high as 85 or 100-plus, you may be wondering which SPF is best.

To get what SPF is all about, it helps to know some other solar lingo. The sun shines down with two types of harmful rays:

Ultraviolet A (UVA). These rays pierce into your skin’s deeper levels, suppress your immune system and cause wrinkles and other signs of aging. (Think A for “age.”)

Ultraviolet B (UVB). These rays, on the other hand, cause sunburns. (Think B for “burn.”)

Both UVA and UVB contribute to skin cancer risk.

SPF measures sunscreen’s ability to block UVB rays. It’s calculated by measuring how long skin covered in sunscreen takes to burn. However, the formula is not straightforward—for instance, SPF 15 blocks 93% of UVB rays and SPF 30 blocks 97%.

Since no product is 100% effective, super-high numbers offer little extra benefit. That said, most experts suggest selecting at least a 30. What’s more, the SPF rating can’t tell you how well the product bars UVA rays.

Seek Broad Protection

The U.S. Food and Drug Administration has proposed a UVA rating system for sunscreen labels. Until it goes into effect, experts recommend seeking products marked “broad-spectrum.”

What else should you locate on labels? The American Academy of Dermatology suggests selecting a water-resistant formula.

Choose, Then Use, Wisely

Buying sun protection is only the first step. A recent survey found most Americans don’t know when, how much or how often to apply it. Rub on 1 ounce—enough to fill a shot glass:

Between 30 minutes and two hours before going outside

Every two hours, or every 80 minutes if you’re swimming or sweating

Even on cloudy days or when you’re indoors and exposed to the sun. UVA rays can penetrate glass windows

Also, be careful about how much sun exposure you get. If possible, stay in the shade between 10 a.m. and 4 p.m. When you’re in the sun, keep your skin covered and wear a wide-brimmed hat when it’s sunny.

Does Sunscreen Affect Your Body’s Vitamin D?

Vitamin D is vital to bone and overall health. It promotes calcium absorption, which strengthens bone.

Sunshine naturally causes vitamin D production in the skin. Just five to 30 minutes of sun, two to three times a week, is enough for most people. But if SPF is blocking your skin from the sun, is that enough for your body to produce vitamin D?

Recent research indicates yes. While it’s true that blocking ultraviolet rays can limit the amount of vitamin D our bodies produce, most studies find that the effect is minimal. In other words, concern over vitamin D production does not warrant going without sunscreen coverage.

That said, if you’re worried about your body’ vitamin D production, the best way to get more is to change your diet. Try milk that’s fortified with vitamin D. Just one cup of milk provides 25% of your daily need. Vitamin D also is found naturally, in varying amounts, in oily fish (such as herring, salmon and sardines), egg yolks and liver.

Sources: American Academy of Dermatology, Institute of Medicine, National Institutes of Health, The New York Times, Krames Staywell, U.S. Food and Drug Administration